The present invention relates to a method for imparting improved surface properties to carbon fibers or, more particularly, to a method for imparting improved susceptibility to adhesive bonding with other materials such as synthetic resins to the surface of carbon fibers.
As is known, carbon fibers are widely used in various fields by virtue of their excellent mechanical strengths, high elastic modulus, heat resistance, corrosion resistance, electric conductivity, lightness and other properties as a material for construction of aircrafts and automobiles, electric and electronic parts, sporting goods and the like. For example, carbon fibers are characteristically useful as a reinforcing material in various kinds of so-called composite materials as combined with a synthetic resin as the matrix. One of the problems in such an application of carbon fibers is the poor adhesive bonding between the surface of the carbon fiber and the matrix resin depending on the types of the resin. A solution for such a problem has been obtained by the treatment of priming or pre-coating of the carbon fibers with another synthetic resin capable of being strongly bonded to both of the carbon fibers and the matrix resin although the results obtained by such a pretreatment is not always satisfactory so that it has long been desired to develop a novel and efficient method for imparting improved surface properties or, in particular, susceptibility to adhesive bonding to the surface of carbon fibers.
As is generally understood, the mechanical strengths, electric properties and other properties of composite materials composed of a synthetic resin as the matrix and a reinforcing material such as carbon fibers depend largely on the strength of adhesive bonding between the matrix resin and the surface of the reinforcing material so that the improvement of carbon fibers in connection with the susceptibility to adhesive bonding on the surface has been a matter of great concern in the fields of industries where the performance of reinforced composite materials is a key factor. Accordingly, the inventors have conducted extensive investigations to develop a novel and improved method therefor and arrived at a discovery leading to the completion of the present invention described below.